A switch must set up connections between its access ports. In the special case of a distributor, these connections are semipermanent. A switch is modular in structure. The access ports are generally distributed over a plurality of electronic circuit cards referred to as "couplers". In general, it is possible to add coupler cards in order to increase the capacity of a switch.
Conventionally, couplers are interconnected by means of a bus for the purpose of transferring data from one coupler to another. Possibly, a redundant second bus is provided to remedy failure of the first bus.
Another architecture is known, in particular from French patent application No. 2 665 314, in which each coupler is connected via an independent both-way link to each of the other couplers. in other words, there is one link for each combination of two couplers. Those links are implemented by means of a backplane having a large number of layers. Each coupler may be backed-up by another coupler in the event of failure. Since that architecture does not have a bus that is common to all of the couplers, it avoids any possibility of blocking due to excess traffic in any given direction, and it also avoids any possibility of the entire switch being blocked by one of the couplers operating wrongly. The present invention relates more particularly to that type of switch.
In that type of switch, forwarding from one access port to another takes place over a path that passes via two couplers. When a coupler is added, when a coupler is removed, and when a coupler breaks down partially or completely, it is necessary for all of the possible paths to be determined anew. In order to enable the paths to be determined in real time, it is necessary for path determination to be performed automatically, i.e. without requiring a human operator to intervene. Also, it is desirable for the means used to be capable of being protected against the possibility of failure in a resource that is used for path determination.